If / Else, Making Decisions

Teach your program to choose different paths based on conditions

Programs need to make decisions. "If this is true, do this. Otherwise, do that." That's what if/else is for.

How would you approach this? Think first, then expand.

Basic if/elsepython

age = 18

if age >= 18:
    print("You can vote!")
else:
    print("Too young to vote.")

🔍Code TracerStep 1 / 7

trace.py

1score = 85←

2if score >= 90:

3 grade = "A"

4elif score >= 80:

5 grade = "B"

6else:

7 grade = "C"

8print(grade)

Variables

No variables yet

Step 1 / 7

Indentation matters in Python. The code inside if and else must be indented (4 spaces or 1 tab). This is how Python knows what's "inside" each branch.

Multiple conditions with elifpython

score = 75

if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
else:
    print("F")
# prints: C

Comparison operators:

== equal to

!= not equal to

> greater than

< less than

>= greater than or equal

<= less than or equal

= assigns a value (x = 5). == checks equality (x == 5). Mixing these up is the #1 beginner mistake.

🌍In the Real World...

Every CI/CD pipeline has conditions: if branch == "main", deploy to prod. If tests fail, stop the pipeline. If image size > 500MB, send an alert. You'll write these daily.

Practice Exercises

0/3 solved

Exercise 1 of 3easy

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Grade Calculator

Write a function get_grade(score) that returns a letter grade:- 90-100 → "A"- 80-89 → "B"- 70-79 → "C"- 60-69 → "D"- Below 60 → "F"

solution.py

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Exercise 2 of 3medium

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FizzBuzz

Write a function fizzbuzz(n) that returns:- "FizzBuzz" if n is divisible by both 3 and 5- "Fizz" if divisible by 3 only- "Buzz" if divisible by 5 only- The number as a string otherwise
This is one of the most famous interview questions!

solution.py

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Exercise 3 of 3medium

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Leap Year

Write a function is_leap_year(year) that returns True if it's a leap year.
A year is a leap year if:- It's divisible by 4 AND- Not divisible by 100, UNLESS also divisible by 400
Examples: 2000 → True, 1900 → False, 2024 → True, 2023 → False

solution.py

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